Production of reactant sheets for developing colorless dye images

ABSTRACT

Bond-like reactant sheets for use developing colored images on the surfaces thereof formed from colorless dyes are produced by applying to a paper substrate a volatile organic solvent solution of phenol-formaldehyde polymer and quickly evaporating the solvent before substantial penetration of the paper substrate, whereby a uniform discontinuous film of said polymer is formed on the exposed surface of the top layer of fibers or pigments particles of said substrate, said dried polymer film being applied at the rate of 0.01 to 0.2 pound per 1,300 square feet of surface. A preferred method of applying said solvent solution of phenol-formaldehyde polymer is by modified offset gravure printing means.

I United States Patent 1151 3,653,945

Davis et al. 1451 Apr. 4, 1972 541 PRODUCTION OF REACTANT SHEETS3,296,965 l/l967 Reif et al. ..1 17/1715 FOR DEVELOPING COLQRLESS DYE2,972,547 2/1921 Tien 17/362 IMAGES 3,020,170 2/19 2 Macaulay...l17/36.2 3,322,557 5/1967 Schwab ..117/362 [72] Inventors: Gerald T.Davis; Robert A. Fetters, both 3,427,180 2/1969 Phillips.. ..ll7/l55ofChillicothe, Ohio 3,451,338 6/1969 Baum 1 1 1 17/3612 1 3,466,1849/1969 Bowler et a1 17/362 [73] Assgnee' The Mead Cmpmmnt Dayton Ohm3,466,185 9/1969 ra 16r ..117/155 L [22] Filed: Oct. 29, 1970 PrimaryExaminer-William D. Martin [21] APP! 85242 Assistant Examiner-M.Sofocleous Related U S Application Data Attorneylrvin V. Gleim, EdwardM. Tritle and Francis M.

Crawford [63] Continuation-in-part of Ser. No. 610,766, Jan. 23,

1967. [57] ABSTRACT [57] U 5. Cl 117/36 2 117/36 8 [17/38 Bond-likereactant sheets for use developing colored images 17/4] i7/155 on thesurfaces thereof formed from colorless dyes are l 1 1 Int. Cl. 841m 5/22produced by applying to a paper substrate a volatile organic g Field L36 8 solvent solution of phenol-formaldehyde polymer and quickly 1evaporating the solvent before substantial penetration of the papersubstrate, whereby a uniform dliscontinuous film of said [56] Referencescued polymer is formed on the exposed surface of the top layer of fibersor pigments particles of said substrate, said dried UNlTED STATESPATENTS polymer film being applied at the rate of0.0l to 0.2 pound per1,300 square feet of surface. A preferred method of applying 3,244,5494/1966 Farnham et a1 ..1 17/362 said Solvent Solution f h l f ld h dpolymer is by 2 1 v 4 6 1 modified offset gravure printing means vrm3,374,768 3/1968 Lawes et al. ..1 17/175 6 Claims, N0 DrawingsPRODUCTION OF REACTANT SHEETS FOR DEVELOPING COLORLESS DYE IMAGES Thisapplication is a continuation-in-part of our US. Pat Ser. No. 610,766,filed Jan. 23, 1967.

This invention relates to the production of a reactant sheet for use asa receiving and color developing sheet for colorless dye images and to amethod of developing such images.

Reactant sheets of this type are usuallyused in conjunction with atransfer sheet which contains a colorless marking ink such as crystalviolet lactone dissolved in a carrier liquid such as chlorinateddiphenyl. A pressure image such as is produced by the striking of atypewriter key releases, in areas where the pressure isapplied, a smallamount of colorless marking ink and transfers it to the surface of thereceiving sheet. A colored image develops in the areas where the markingink is transferred to the reactant sheet. Such a reactant sheet andprocess for making it are described in U. 5.. Pat. No. 2,699,432 issuedto Marra .et al. In this patent, a reactive pigment such as attapulgite(attapulgus clay) or a zeolitic material is dispersedin an aqueousbinder composition containing .ammonium caseinate, sodium silicate, anda butadiene-styrene copolymer latex. The pigmented coating composition,when coated and dried on a paper base, produces a blue mark where it iscontacted by a colorless marking ink containing crystal violet lactone.In general, it is necessary to apply 2 to 3 pounds or more per ream(1,300 square feet) of the above dried coating to paper in order tofully develop the colorless dye.

The necessity of using such heavy coatings on paper has a detrimentaleffect on the strength properties and appearance and feel of the paper.This is particularly so where extremely thin papers are desired as theweight of the coating may be as much as 30 percent of the total paperweight. Thin papers of high strengths are necessary in the production ofmanifold forms where the paper is subjected to punching, perforating,folding and collating operations.

Incorporation of a reactive pigment into the paper at the wet end of thepapermachine has also been tried but has not been commerciallysuccessful since large amounts of pigment, at least 16 percent of thefinished paper weight, were required to produce a satisfactory coloredmark with a colorless marking ink. The presence of the reactive pigmentin the paper had a detrimental effect on the strength and agingproperties ofthe paper. Furthermore, the bulk of the reactant pigmentwas not on the surface of the paper and, thus, sharp and clear imageswere not produced.

It has been found that a relatively uniform thin coating of a solidphenolic reactant can be applied to a paper base by contacting saidpaper base with a thin film ofa solution consisting essentially of saidphenolic reactant in a volatile organic solvent and immediatelyevaporating said solvent before substantial penetration into the paperbase takes place and so that said phenolic reactant is retainedessentially completely on the contacted surface of the paper base.Thusly applied, the phenolic reactant is readily available for reactionwith a colorless dye and it has been found that well defined coloredmarks are formed on the surface of the paper base on marking the surfacewith a colorless marking ink containing a colorless dye dissolved in acarrier liquid without any substantial marking showing on the reverseside of the sheet.

The amount of phenolic reactant coating necessary to produce asatisfactory mark is in the range of 0.01 to .0.2 pound per ream of1,300 square feet, depending somewhat on the particular phenolicreactant used, which amount is found to give uniform, discontinuousfilmofphenolicpolymer on the surface of said sheet. Such a small amount ofcoating does not materially affect the properties, particularly thestrength, handling and printing properties, of the paperbase to which itis applied. Thus, reactant sheets resembling light weightbond papers maybe produced, whereas it was necessary to coat the ,prior art mechanicalsheets with 2 to 3 pounds per ream of reactant coating to obtaincommercially acceptable ,paper. Such coated prior art reactant sheetsdonot have the handling and printing properties of bond papers and thestrength properties for the same weight ofpaper are considerably less.

Accordingly, it is an object of this invention to provide a reactantsheet for developing colorlessdye images having improved strength,handling and printingproperties.

Another object of the invention is to provide a reactant sheet in whicha phenolic reactant is essentially completely retained on the papersurface and is readily available for developing colorless dye imagesapplied thereon.

It is another object of the invention to provide a method of making theabove reactant sheet.

A further object of the inventionis to provide a method of producing acolored image on the surface of a reactant sheet having improvedstrength, handling and printing properties over those of prior artreactant sheets.

The color developing reactants used in the present invention areessentially solid, non-volatile, water insoluble, fusible phenolicpolymers. Such materials must be capable of reacting with a colorlessdye dissolved in a carrier liquid to produce a colored material. Since.the color is developed only on intimate molecular contact. of thephenolicmaterials with the colorless dye, the phenolic materials must'besoluble at least in limited amounts in the carrier'liquid. They alsoshould be chemically stable and particularly non-reactive toward thepapermaking chemicals present in the paper base. It is also desirablethat the phenolic materials are relatively colorless and that theyshould not discolor with age. Suitable phenolic polymers arecharacterized by havingat least one position ortho to the phenolic OHgroup occupied by a hydrogen, halogen, hydroxyl, methyl or methylenegroup. A preferred group of phenolic materials are the para substitutedphenol formaldehyde novolak condensation polymers, for example, aparaphenylphenol formaldehyde condensation polymer having .a ring andball softening point of to 225 F. Other suitable compounds of this typeinclude novolak condensation polymers of paraalkylphenol-formaldehyde,where the alkyl radical contains four to eight carbon atoms,parachlorophenol-formaldehyde, orthochlorophenol-formaldehyde, and themixed novolak condensation polymers of parachloro-paraalkylphenols.in1:1 to 3:1 mol ratio with formaldehyde, and mixtures of said polymers.

The colorless dyes may be selected from certain of the quinoid ionictype dies, particularly various lactone, lactam, or auramine leuco dyessuch as, for example, crystal violet lactone, malachite green lactone,1, l-bis(para amino-phenyl) phthalen and 2, 5 dichlorophenyl leucoauramine.

The reactant coating composition is essentially a solution of thephenolic polymer in a volatile organic solvent. The solvent shouldbefast drying and should preferably dissolve up to an equal amount ofthe phenolic polymer so that the desired amounts of dried phenolicmaterials can be obtained by applying the thin wet films of thethickness specified by this invention. Such fast drying solvents includetoluene, xylene, isopropryl alcohol, ethyl alcohol, acetone, methylethyl ketone and butyl acetate.

The phenolic coating composition may be applied to the paper base by anymethod whereby there is obtained a uniform wet film of the coatingcomposition of the required composition having a thicknessofsubstantially not more than 2X IOfinches. This corresponds to a wet filmas applied to the paper having athickness of 1X10 inches. Above thislimit,

the phenolic coatingcomposition will penetrate the paper base. Forexample, penetration of a 15 ;pound form bond paper occurred whencontacted with a wetfilm of phenolic coating composition (50 percentp-phenylphenol aldehyde condensate solution in toluene) having athickness of 2.8Xl0 inches and a film having the desiredproperties wasnot obtained.

means. The phenolic coating composition is metered onto an etched orengraved gravure roll by passing through a pressure nip formed by thegravure roll and a hard surfaced roll, i.e. hard rubber roll. Meteredfilm is then transferred in part by rolling pressure contact to a rollof softer composition; Le. a soft rubber roll, from which it istransferred to the surface of the paper base by rolling pressure contacttherewith. The pressure between the soft rubber roll and roll backingthe paper is not critical but is of a low order, being just sufficientto establish positive uniform contact of the film of coating with thesurface of the paper base.

Using the thin wet films of this invention and fast drying solvents, thesolvent portion of the coating composition, whether by air drying oroven drying, is evaporated so quickly that penetration of phenolicpolymer into the base is essentially eliminated. Thin coatings ofphenolic polymer have been applied to as widely diversified papersurfaces as porous filter paper and a dense pigment coated printingpaper. Examina tion of the above coated papers showed that in all casesphenolic polymer was tightly adhered to and essentially completelyretained on the exposed surfaces of the top layer of fibers or pigmentparticles, in the form ofa uniform, discontinuous film. Both of theabove phenolic coated papers gave well defined colored images whentested with a colorless marking ink containing crystal violet lactone.

The concentration of phenolic polymer in the coating composition doesnot affect penetration of the composition into a paper base when appliedby the method of the present invenphenolic coating composition low, infact below that which causes an excess of liquid composition over thatwhich is in the recesses of the gravure roll to pass between the hardrubber roll and the gravure roll.

By way of illustration, but not by way of limiting the scope oftheinvention, the following examples are set forth.

EXAMPLE 1 A 15 pound per ream uncoated form bond paper containing about6 percent clay filler was coated at 800 feet per minute using offsetgravure printing means as previously described. A l7.2 percent solutionof paraphenylphenol formaldehyde condensate in toluene was applied in awet film thickness of about 7.3 l inches and dried in a forced air ovenat I82 F. to

give a dried coating ofcondensate of0.074 pound per ream on the surfaceof the paper.

EXAMPLE 2 Prior art, Reactant sheet A ttapulgus prepared by reactantExample Example bond Properties sheet 1 .2 paper Basis weight (1300 sq.ft.) 1G. 4 15.3 14.5 15.3

Burst Factor 11M .34. 2 25.0 23.6 Tear factor:

Calender intensity 50. 0 54. 6 57. U r

Typewriter intensity 62. 7 63, 2 65. S)

Legibility of typed characters 4 Good Good Good NOTE l.- The perforationstrength was determined by the method described in U.S. Patent No.3,099,153.

NOTE 2.Calendcr intensity is a contrast ratio whereas the lower thenumerical values, the greater the intcnsity of color. This value isdetermined by placing the coated side of a reactant paper to be testedin contact with the coated side of a standardized transfer sheet, suchas is describcd in 11.8. Patent 2,711,375 granted to Robert W. Sandbcrgon June 21, 1955, and then pa sing the superimposed papers through acalender machine, the rolls of which are subjected to a known standardload. A Bausch & Lomb Opacimctcr is employed to obtain at least threemeasurements of the percent reflectance of the printed and unprintedareas of the reactant paper seconds after calendaring and the results ofsuch measurements are averaged. The calender intensity ratio in per centis then calculated according to the formula:

average printed area reflectance Calender intensity: x 100.

average non-printed area reflectance NOTE 3.-Typcwriter intensity is acontrast ratio similar to calender intensity. It is determined in asimilar way to calender intensity except that instead of passing thesuperimposed transfer and reactant paper through a calender, closelyspaced ms are typed on the superimposed papers using a special electrictypewriter with no ribbon and the opaei meter readings are made on thereactant paper 20 minutes after typing.

NOTE 4.'Ihis is a subjective test made by typing on a transfer sheetsuperimposed on a reactant sheet and judging the appearance of the typedreproduction.

tion. Coating compositions containing from 1 to 40 percent of a phenolicpolymer, a paraphenylphenol formaldehyde polymeric condensate, intoluene were applied to a form bond paper without observable penetrationof phenolic polymer. The preferred amount of paraphenylphenol is 0.02 to0.2 pound per ream. Both above and below this amount, the intensity ofthe colored mark is poorer than within the preferred range.

At the wet film thicknesses used in the process of the presentinvention, viscosity of the phenolic coating composition does not affectthe penetration of phenolic polymer. However, it has been found thatusing the preferred method of Coating of the form bond paper with thephenolic polymers has no significant effect on the strength propertiesof the paper.

The superior strength properties of the paper coated withparaphenylphenol formaldehyde condensate as prepared in Examples l and 2over those of the prior art attapulgus clay coated sheet are apparentfrom a comparison of the burst, tear, stiffness and perforation strengthresults. The legibility of the typed characters is equivalent to thatproduced on the prior art reactant sheet. The calender and typewriterintensity of the reactant sheet produced by Example 1 were 54.6 and63.2, respectively, as compared to 50.0 and 62.7 for the prior thepresent invention, it is preferred to keep viscosity of the art sheet.Calendering of the reactant sheet of Example 1 to a 90 Sheffieldsmoothness, as compared to the prior art sheet smoothness of 93,produced a reactant sheet with calender and typewriter values intensityof52.3 and 62.5, respectively The handling and printing properties ofthe reactant sheet prepared in Example 1, when run on an offset formpress and subsequently collated, were found to be the same as for theuncoated form bond paper.

Since the examples described are for the purposes of illustration only,it is to be understood that the present invention includes allmodifications and equivalents which fall within the scope of theinvention as defined by the appended claims.

What is claimed is:

l. A method of preparing a bond-like reactant sheet for use indeveloping a colorless image formed thereon from colorless dye dissolvedin a carrier liquid, which comprises the steps of uniformly coating thesurface of one side of a paper substrate with a thin film of a volatileorganic solvent solution of an essentially solid, nonvolatile,water-insoluble, fusible phenolformaldehyde condensation polymer capableof reacting with colorless dyes to form a colored material, in an amountsufficient to give (Mil to 0.2 pound of said solid polymer per 1,300square feet of said paper substrate, immediately evaporating the solventused to apply said polymer bel'ore substantial penetration ot'said paperbase takes place, whereby a substantially uniform discontinuous lilm ofsaid polymer is left on the surface olsaid paper base.

2. A method according to claim I, wherein the wet film of coatingapplied to said paper substrate has a thickness of not substantiallygreater than 2 X inches.

3. A method according to claim 1, wherein said polymer is a substitutedphenolformaldehyde novolak condensation product in which at least onegroup ortho to the phenolic OH group is a hydrogen, hydroxyl, halogen,methyl or methylene group.

4. A method according to claim 1, wherein said polymer is selected fromnovolak condensation polymers of paraalkylphenol formaldehyde where thealkyl radical contains four to eight carbon atoms,parachlorophenol-formaldehyde, orthochlorophenol-formaldehyde,paraphenyl-formaldehyde, and the mixed novolak condensation polymers ofparachloroparalkylphenols in 1:1 to 3:1 mol ratio with formaldehyde, andmixtures of said polymers.

5, A method according to claim 1, wherein said'volatile organic solventsolution of said phenol-formaldehyde polymer is applied to said papersubstrate by a modified offset gravure printing means whereby saidsolution is metered onto an etched or engraved gravure roll from whichit is then transferred by rolling pressure contact to a roll of softercomposition from which the film of solution is transferred to the paperbase substrate by rolling pressure contact therewith.

6. The method according to claim I, characterized in that the solventfor said phenolic polymer is selected from the group of fast dryingsolvents consisting of toluene, xylene, isopropyl alcohol, ethylalcohol, acetone, methyl ethyl kctone and butyl acetate.

2. A method according to claim 1, wherein the wet film of coatingapplied to said paper substrate has a thickness of not substantiallygreater than 2 X 10 4 inches.
 3. A method according to claim 1, whereinsaid polymer is a substituted phenol-formaldehyde novolak condensationproduct in which at least one group ortho to the phenolic OH group is ahydrogen, hydroxyl, halogen, methyl or methylene group.
 4. A methodaccording to claim 1, wherein said polymer is selected from novolakcondensation polymers of paraalkylphenol formaldehyde where the alkylradical contains four to eight carbon atoms,parachlorophenol-formaldehyde, orthochlorophenol-formaldehyde,paraphenyl-formaldehyde, and the mixed novolak condensation polymers ofparachloroparalkylphenols in 1:1 to 3:1 mol ratio with formaldehyde, andmixtures of said polymers.
 5. A method according to claim 1, whereinsaid volatile organic solvent solution of said phenol-formaldehydepolymer is applied to said paper substrate by a modified offset gravureprinting means whereby said solution is metered onto an etched orengraved gravure roll from which it is then transferred by rollingpressure contact to a roll of softer composition from which the film ofsolution is transferred to the paper base substrate by rolling pressurecontact therewith.
 6. The method according to claim 1, characterized inthat the solvent for said phenolic polymer is selected from the group offast drying solvents consisting of toluene, xylene, isopropyl alcohol,ethyl alcohol, acetone, methyl ethyl ketone and butyl acetate.